Navy Yard Shooter Wrote "Better Off This Way" on Gun

Aaron Alexis' mother speaks as police release new information about the shooting.
2:14 | 09/19/13

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Transcript for Navy Yard Shooter Wrote "Better Off This Way" on Gun
Now, we have new details emerging about the washington navy yard shooter. Abc news learning that aaron alexis carved two images -- two messages into the side of his gun. And now, his mother has spoken out with an emotional message. Abc's pierre thomas joins us from washington this morning with the very latest. Good morning, pierre. Reporter: Good morning, robin. Today, the fbi is trying to unravel the mystery of motive. As you said, they have a tantalizing new clue. This morning, authorities are studying the phrases that aaron alexis carved into his shotgun, used to carry out the deadly attack in the washington navy yard. Sources tell abc news, alexis etched the words, better off this way, and my e.L.F. Weapon, on the stock of the shotgun. Investigators want to know if better off this way, was a signal alexis expected to die during the massacre. There was probably multiple triggers that caused him to decide, now's the time I'm going to take this course of action. Thinking about it, conceptualizing it, planning it in his head. Reporter: As for e.L.F., Some investigators suspect it might refer to the tech phrase, extremely low frequency. Alexis worked as a computer technician. And ran into police about hearing voices and microwave machines bombarding his body. He told that story to police. But the navy confirmed it was never passed up the chain of command. He kept his job with the navy and his secret security clearance. Obviously, there were a lot of red flags. And where there are failures, we will correct them. Reporter: We're also hearing for the first time, someone who appears truly sorry. The killer's mother. Aaron is now in a place where he can no longer do harm to anyone. I am so, so very sorry that this has happened. My heart is broken. Reporter: The navy yard reopens today. But for the families of the dead and wounded, the pain is still raw. Robin, so many shattered lives. Absolutely. And the mother spoke mostly about the victims, not so much about her son in that message. We're going to turn to the

This transcript has been automatically generated and may not be 100% accurate.

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